This invention relates to a pneumatically operated stone-working apparatus, such as a hammer drill which incorporates an arrangement directing a liquid spray to the work area and which includes a manually operated lever for actuating a valve plunger rotatable into open and closed positions for controlling the admission of the compressed gas to the tool drive.
In conventional power tools of the above-outlined type the risks are high that the worker, contrary to operating instructions, starts the tool drive before activating the spraying device or continues the stone-working operation during periods when the liquid spraying, for some reason, no longer takes place. The purpose of the spraying operation is to bind the dust generated during the stone working. The above-noted occurrences represent serious health hazards which, after a long while, manifest themselves mostly as silicose sickness.